U.S. patent application number 11/987830 was filed with the patent office on 2008-06-05 for white light emitting device and white light source module using the same.
This patent application is currently assigned to SAMSUNG ELECTRO-MECHANICS CO., LTD.. Invention is credited to Hun Joo Hahm, Seong Yeon Han, Ho Yeon Kim, Hyung Suk Kim, Young Sam Park, Young June Yeong, Chul Hee Yoo.
Application Number | 20080128735 11/987830 |
Document ID | / |
Family ID | 39474687 |
Filed Date | 2008-06-05 |
United States Patent
Application |
20080128735 |
Kind Code |
A1 |
Yoo; Chul Hee ; et
al. |
June 5, 2008 |
White light emitting device and white light source module using the
same
Abstract
A white light emitting device including: a blue light emitting
diode chip having a dominant wavelength of 443 to 455 nm; a red
phosphor disposed around the blue light emitting diode chip, the
red phosphor excited by the blue light emitting diode chip to emit
red light; and a green phosphor disposed around the blue light
emitting diode chip, the green phosphor excited by the blue light
emitting diode chip to emit green light, wherein the red light
emitted from the red phosphor has a color coordinate falling within
a space defined by four coordinate points (0.5448, 0.4544),
(0.7079, 0.2920), (0.6427, 0.2905) and (0.4794, 0.4633) based on
the CIE 1931 chromaticity diagram, and the green light emitted from
the green phosphor has a color coordinate falling within a space
defined by four coordinate points (0.1270, 0.8037), (0.4117,
0.5861), (0.4197, 0.5316) and (0.2555, 0.5030) based on the CIE
1931 color chromaticity diagram.
Inventors: |
Yoo; Chul Hee; (Suwon,
KR) ; Yeong; Young June; (Suwon, KR) ; Park;
Young Sam; (Seoul, KR) ; Han; Seong Yeon;
(Gwangju, KR) ; Kim; Ho Yeon; (Incheon, KR)
; Hahm; Hun Joo; (Sungnam, KR) ; Kim; Hyung
Suk; (Suwon, KR) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
600 13TH STREET, N.W.
WASHINGTON
DC
20005-3096
US
|
Assignee: |
SAMSUNG ELECTRO-MECHANICS CO.,
LTD.
|
Family ID: |
39474687 |
Appl. No.: |
11/987830 |
Filed: |
December 5, 2007 |
Current U.S.
Class: |
257/98 ;
257/E33.061 |
Current CPC
Class: |
Y02B 20/181 20130101;
H01L 33/504 20130101; H05B 33/12 20130101; C09K 11/0883 20130101;
C09K 11/7734 20130101; C09K 11/7731 20130101; F21K 9/00 20130101;
G02F 1/133609 20130101; Y02B 20/00 20130101; G02F 1/133603
20130101 |
Class at
Publication: |
257/98 ;
257/E33.061 |
International
Class: |
H01L 33/00 20060101
H01L033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 5, 2006 |
KR |
10-2006-0122631 |
Feb 6, 2007 |
KR |
10-2007-0012112 |
Claims
1. A white light emitting device comprising: a blue light emitting
diode chip having a dominant wavelength of 443 to 455 nm; a red
phosphor disposed around the blue light emitting diode chip, the
red phosphor excited by the blue light emitting diode chip to emit
red light; and a green phosphor disposed around the blue light
emitting diode chip, the green phosphor excited by the blue light
emitting diode chip to emit green light, wherein the red light
emitted from the red phosphor has a color coordinate falling within
a space defined by four coordinate points (0.5448, 0.4544),
(0.7079, 0.2920), (0.6427, 0.2905) and (0.4794, 0.4633) based on
the CIE 1931 chromaticity diagram, and the green light emitted from
the green phosphor has a color coordinate falling within a space
defined by four coordinate points (0.1270, 0.8037), (0.4117,
0.5861), (0.4197, 0.5316) and (0.2555, 0.5030) based on the CIE
1931 color chromaticity diagram.
2. The white light emitting device of claim 1, wherein the blue
light emitting diode chip has a full width at half-maximum of 10 to
30 nm, the green phosphor has a full width at half-maximum of 30 to
100 nm and the red phosphor has a full width at half-maximum of 50
to 200 nm.
3. The white light emitting device of claim 1, wherein the red
phosphor comprises at least one of CaAlSiN.sub.3:Eu and
(Ca,Sr)S:Eu.
4. The white light emitting device of claim 1, wherein the green
phosphor comprises at least one of A.sub.2SiO.sub.4:Eu,
SrGa.sub.2S.sub.4:Eu and .beta.-SiAlON, wherein A in
A.sub.2SiO.sub.4:Eu comprises at least one of Ba, Sr and Ca.
5. The white light emitting device of claim 1, further comprising a
resin encapsulant encapsulating the blue light emitting diode chip,
wherein the green phosphor and the red phosphor are dispersed in
the resin encapsulant.
6. The white light emitting device of claim 1, further comprising a
resin encapsulant encapsulating the blue light emitting diode chip,
wherein a first phosphor film comprising one of the green and red
phosphors is formed along a surface of the blue light emitting
diode chip between the green light emitting device chip and the
resin encapsulant, and a second phosphor film comprising the other
one of the green and red phosphors is formed on the resin
encapsulant.
7. A white light source module comprising: a circuit board; a blue
light emitting diode chip disposed on the circuit board and having
a dominant wavelength of 443 to 455 nm; a red phosphor disposed
around the blue light emitting diode chip, the red phosphor excited
by the blue light emitting diode chip to emit red light; and a
green phosphor disposed around the blue light emitting diode chip,
the green phosphor excited by the blue light emitting diode chip to
emit green light, wherein the red light emitted from the red
phosphor has a color coordinate falling within a space defined by
four coordinate points (0.5448, 0.4544), (0.7079, 0.2920), (0.6427,
0.2905) and (0.4794, 0.4633) based on the CIE 1931 color
chromaticity diagram, and the green light emitted from the green
phosphor has a color coordinate falling within a space defined by
four coordinate points (0.1270, 0.8037), (0.4117, 0.5861), (0.4197,
0.5316) and (0.2555, 0.5030) based on the CIE 1931 color
chromaticity diagram.
8. The white light source module of claim 7, wherein the blue light
emitting diode chip has a full width at half-maximum of 10 to 30
nm, the green phosphor has a full width at half-maximum of 30 to
100 nm and the red phosphor has a full width at half-maximum of 50
to 200 nm.
9. The white light source module of claim 7, wherein the red
phosphor comprises at least one of CaAlSiN.sub.3:Eu and
(Ca,Sr)S:Eu.
10. The white light source module of claim 7, wherein the green
phosphor comprises at least one of A.sub.2SiO.sub.4:Eu,
SrGa.sub.2S.sub.4:Eu and .beta.-SiAlON, wherein A in
A.sub.2SiO.sub.4:Eu comprises at least one of Ba, Sr and Ca.
11. The white light source module of claim 7, further comprising a
resin encapsulant encapsulating the blue light emitting diode chip,
wherein the blue light emitting diode chip is directly mounted on
the circuit board.
12. The white light source module of claim 7, further comprising a
package body mounted on the circuit board, the package body
defining a reflective cup, wherein the blue light emitting diode
chip is mounted in the reflective cup defined by the package
body.
13. The white light source module of claim 12, further comprising a
resin encapsulant formed inside the reflective cup defined by the
package body, the encapsulant encapsulating the blue light emitting
diode chip.
14. The white light source module of claim 7, further comprising a
resin encapsulant encapsulating the blue light emitting diode chip,
wherein the green phosphor and the red phosphor are dispersed in
the resin encapsulant.
15. The white light source module of claim 7, further comprising a
resin encapsulant encapsulating the blue light emitting device
chip, wherein a first phosphor film comprising one of the green and
red phosphors is formed along a surface of the blue light emitting
diode chip between the blue light emitting diode chip and the resin
encapsulant, and a second phosphor film comprising the other one of
the green and red phosphors is formed on the resin encapsulant.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the priority of Korean Patent
Application Nos. 2006-122631 filed on Dec. 5, 2007 and 2007-12112
filed on Feb. 6, 2007, in the Korean Intellectual Property Office,
the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a white light emitting
device and a white light source module using the same, and more
particularly, to a white light emitting device beneficially
applicable to a backlight unit of a liquid crystal display to
ensure high color reproducibility, and a white light source module
using the same.
[0004] 2. Description of the Related Art
[0005] Recently, a light emitting diode (LED) is highlighted as a
light source of a backlight unit (BLU) employed in liquid crystal
displays such as lap top computers, monitors, mobile phones and
TVs. A cold cathode fluorescent lamp (CCFL) has been in use as a
white light source of the BLU, but lately, a white light source
module using the LED has captured attention due to its advantages
such as better color representation, environment friendliness,
higher performance and lower power consumption.
[0006] In a conventional white light source module for the BLU, a
blue LED, a green LED and a red LED are arranged on a circuit
board. FIG. 1 illustrates an example of such arrangement. Referring
to FIG. 1, a white light source module 10 for a BLU includes a red
R LED 12, a green G LED 14 and a blue LED 16 arranged on a circuit
board 11 such as a printed circuit board. The R, G, and B LEDs 12,
14, and 16 may be mounted on the board 11 in a configuration of
packages each including an LED chip of a corresponding color, or
lamps. These R, G, and B LED packages or lamps may be repeatedly
arranged on the board to form an overall white surface or line
light source. As described above, the white light source module 10
employing the R, G, and B LEDs is relatively excellent in color
reproducibility and an overall output light can be controlled by
adjusting a light amount of the R, G, and B LEDs.
[0007] However, in the white light source module 10 described
above, the R, G, and B LEDs 12, 14, and 16 are spaced apart from
another, thereby potentially posing a problem to color uniformity.
Moreover, to produce white light of a unit area, at least a set of
R, G, and B LED chips is required since the three-colored LED chips
constitute a white light emitting device. This entails complicated
circuit configuration for driving and controlling the LED of each
color, thus leading to higher costs for circuits. This also
increases the manufacturing costs for packages and the number of
the LEDs required.
[0008] Alternatively, to implement a white light source module, a
white light emitting device having a blue LED and a yellow phosphor
has been employed. The white light source module utilizing a
combination of the blue LED and yellow phosphor is simple in
circuit configuration and low in price. However, the white light
source module is poor in color reproducibility due to relatively
low light intensity at a long wavelength. Therefore, a
higher-quality and lower-cost LCD requires a white light emitting
device capable of assuring better color reproducibility, and a
white light source module using the same.
[0009] Accordingly, there has been a call for maximum color
reproducibility and stable color uniformity of the white light
emitting device adopting the LED and phosphor, and the white light
source module using the same.
SUMMARY OF THE INVENTION
[0010] An aspect of the present invention provides a white light
emitting device with high color reproducibility and superior color
uniformity.
[0011] An aspect of the present invention also provides a white
light source module with high color reproducibility and superior
color uniformity, which is manufactured with lower costs.
[0012] According to an aspect of the present invention, there is
provided a white light emitting device including: a blue light
emitting diode (LED) chip having a dominant wavelength of 443 to
455 nm; a red phosphor disposed around the blue LED chip, the red
phosphor excited by the blue LED chip to emit red light; and a
green phosphor disposed around the blue LED chip, the green
phosphor excited by the blue LED chip to emit green light, wherein
the red light emitted from the red phosphor has a color coordinate
falling within a space defined by four coordinate points (0.5448,
0.4544), (0.7079, 0.2920), (0.6427, 0.2905) and (0.4794, 0.4633)
based on the CIE 1931 chromaticity diagram, and the green light
emitted from the green phosphor has a color coordinate falling
within a space defined by four coordinate points (0.1270, 0.8037),
(0.4117, 0.5861), (0.4197, 0.5316) and (0.2555, 0.5030) based on
the CIE 1931 color chromaticity diagram.
[0013] The blue LED chip may have a full width at half-maximum
(FWHM) of 10 to 30 nm , the green phosphor may have a FWHM of 30 to
100 nm and the red phosphor may have a FWHM of 50 to 200 nm. The
red phosphor may include at least one of CaAlSiN.sub.3:Eu and
(Ca,Sr)S:Eu. The green phosphor may include at least one of
A.sub.2SiO.sub.4:Eu, SrGa.sub.2S.sub.4:Eu and .beta.-SiAlON,
wherein A in A.sub.2SiO.sub.4:Eu is at least one of Ba, Sr and
Ca.
[0014] The white light emitting device may further include a resin
encapsulant encapsulating the blue LED chip, wherein the green
phosphor and the red phosphor are dispersed in the resin
encapsulant.
[0015] The white light emitting device may further include a resin
encapsulant encapsulating the blue LED chip, wherein a first
phosphor film including one of the green and red phosphors is
formed along a surface of the blue LED chip between the green light
emitting device chip and the resin encapsulant, and a second
phosphor film including the other one of the green and red
phosphors is formed on the resin encapsulant.
[0016] According to another aspect of the present invention, there
is provided a white light source module including: a circuit board;
a blue LED chip disposed on the circuit board and having a dominant
wavelength of 443 to 455 nm; a red phosphor disposed around the
blue LED chip, the red phosphor excited by the blue LED chip to
emit red light; and a green phosphor disposed around the blue LED
chip, the green phosphor excited by the blue LED chip to emit green
light, wherein the red light emitted from the red phosphor has a
color coordinate falling within a space defined by four coordinate
points (0.5448, 0.4544), (0.7079, 0.2920), (0.6427, 0.2905) and
(0.4794, 0.4633) based on the CIE 1931 color chromaticity diagram,
and the green light emitted from the green phosphor has a color
coordinate falling within a space defined by four coordinate points
(0.1270, 0.8037), (0.4117, 0.5861), (0.4197, 0.5316) and (0.2555,
0.5030) based on the CIE 1931 color chromaticity diagram.
[0017] The blue LED chip may have a FWHM of 10 to 30 nm, the green
phosphor may have a FWHM of 30 to 100 nm and the red phosphor may
have a FWHM of 50 to 200 nm. The red phosphor may include at least
one of CaAlSiN.sub.3:Eu and (Ca,Sr)S:Eu. The green phosphor may
include at least one of A.sub.2SiO.sub.4:Eu, SrGa.sub.2S.sub.4:Eu
and .beta.-SiAlON, wherein A in A.sub.2SiO.sub.4:Eu is at least one
of Ba, Sr and Ca.
[0018] The white light source module may further include a resin
encapsulant encapsulating the blue LED chip, wherein the blue LED
chip is directly mounted on the circuit board.
[0019] The white light source module may further include a package
body mounted on the circuit board, the package body defining a
reflective cup, wherein the blue LED chip is mounted in the
reflective cup defined by the package body.
[0020] The white light source module may further include a resin
encapsulant formed inside the reflective cup defined by the package
body, the encapsulant encapsulating the blue LED chip.
[0021] The white light source module may further include a resin
encapsulant encapsulating the blue LED chip, wherein the green
phosphor and the red phosphor are dispersed in the resin
encapsulant.
[0022] The white light source module may further include a resin
encapsulant encapsulating the blue light emitting device chip,
wherein a first phosphor film including one of the green and red
phosphors is formed along a surface of the blue LED chip between
the blue light emitting diode chip and the resin encapsulant, and a
second phosphor film including the other one of the green and red
phosphors is formed on the resin encapsulant.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The above and other aspects, features and other advantages
of the present invention will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
[0024] FIG. 1 is a cross-sectional view illustrating a conventional
white light source module for a backlight unit;
[0025] FIG. 2 is a cross-sectional view illustrating a white light
emitting device and a white light source module according to an
exemplary embodiment of the invention;
[0026] FIG. 3 is a cross-sectional view illustrating a white light
emitting device and a white light source module according to an
exemplary embodiment of the invention;
[0027] FIG. 4 is a cross-sectional view illustrating a white light
emitting device and a white light source module according to an
exemplary embodiment of the invention;
[0028] FIG. 5 is a cross-sectional view illustrating a white light
emitting device and a white light source module according to an
exemplary embodiment of the invention;
[0029] FIG. 6 illustrates a color coordinate space of phosphors
used in a white light emitting device according to an exemplary
embodiment of the invention; and
[0030] FIG. 7 illustrates a color coordinate range obtained in a
case where white light source modules of Inventive Example and
Comparative Example are employed in a backlight unit of a liquid
crystal display (LCD).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0031] Exemplary embodiments of the present invention will now be
described in detail with reference to the accompanying drawings.
This invention may, however, be embodied in many different forms
and should not be construed as limited to the embodiments set forth
herein. Rather, these embodiments are provided so that this
disclosure will be thorough and complete, and will fully convey the
scope of the invention to those skilled in the art. In the
drawings, the shapes and dimensions may be exaggerated for clarity,
and the same reference signs are used to designate the same or
similar components throughout.
[0032] FIG. 2 is a schematic cross-sectional view illustrating a
white light emitting device and a white light source module using
the same according to an exemplary embodiment of the invention.
Referring to FIG. 2, the white light source module 510 includes a
circuit board 101 such as a printed circuit board, and at least one
white light emitting device 100 disposed on the circuit board 101.
The white light emitting device 100 includes a blue B light
emitting diode (LED) chip 103, a green G phosphor 105 and a red R
phosphor 107. The green phosphor 105 and the red phosphor 107 are
excited by the blue LED chip 103 to emit green light and red light,
respectively. The green light and the red light are mixed with a
portion of the blue light from the blue LED chip 103 to produce
white light.
[0033] Particularly, according to the present embodiment, the blue
LED chip 103 is directly mounted on the circuit board 101 and the
phosphors 105 and 107 are dispersed and mixed uniformly in a resin
encapsulant 130 encapsulating the blue LED chip 103. The resin
encapsulant 130 may be formed, for example, in a semi-circle which
serves as a kind of lens. Alternatively, the resin encapsulant 130
may be formed of one of an epoxy resin, a silicone resin and a
hybrid resin. As described above, the blue LED chip 103 is directly
mounted on the circuit board 101 by a chip-on-board technique,
thereby allowing the white light emitting device 100 to achieve a
greater view angle more easily.
[0034] One of an electrode pattern and a circuit pattern (not
shown) is formed on the circuit board 101, and the circuit pattern
is connected to an electrode of the blue LED chip 103 by e.g., wire
bonding or flip chip bonding. This white light source module 510
may include a plurality of the white light emitting devices 100 to
form a surface or line light source with a desired area, thereby
beneficially utilized as a light source of a backlight unit of the
LCD device.
[0035] The inventors of the present invention have defined a
dominant wavelength of the blue LED chip 103 to be in a specific
range and a color coordinate of the red and green phosphors 105 and
107 to be within a specific space based on the CIE 1931 color
chromaticity diagram. This enabled the inventors to realize maximum
color reproducibility from a combination of the green and red
phosphors and the blue LED chip.
[0036] Specifically, to obtain maximum color reproducibility from a
combination of the blue LED chip-green phosphor-red phosphor, the
blue LED chip 103 has a dominant wavelength of 443 to 455 nm. Also,
the red light emitted from the red phosphor 107 excited by the blue
LED chip 103 has a color coordinate falling within a space defined
by four coordinate points (0.5448, 0.4544), (0.7079, 0.2920),
(0.6427, 0.2905) and (0.4794, 0.4633) based on the CIE 1931 (x, y)
color chromaticity diagram. Moreover, the green light emitted from
the green phosphor excited by the blue LED chip 103 has a color
coordinate falling within a space defined by (0.1270, 0.8037),
(0.4117, 0.5861), (0.4197, 0.5316) and (0.2555, 0.5030) based on
the CIE 1931 color chromaticity diagram.
[0037] FIG. 6 illustrates color coordinate spaces of the red and
green phosphors described above. Referring to FIG. 6, the CIE 1931
color chromaticity diagram is marked with a quadrilateral-shaped
spacer composed of four coordinate points (0.5448, 0.4544),
(0.7079, 0.2920), (0.6427, 0.2905) and (0.4794, 0.4633) and a
quadrilateral-shaped space g composed of four coordinate points
(0.1270, 0.8037), (0.4117, 0.5861), (0.4197, 0.5316) and (0.2555,
0.5030). As described above, the red phosphor and green phosphor
are selected such that color coordinates thereof fall within the
quadrilateral-shaped spaces r and g, respectively.
[0038] Here, a dominant wavelength is a wavelength value derived
from a curve obtained by integrating an actually-measured spectrum
graph of an output light of the blue LED chip and a luminosity
curve. The dominant wavelength is a value considering visibility of
a person. This dominant wavelength corresponds to a wavelength
value at a point where a line connecting a center point (0.333,
0.333) of the CIE 1976 color chromaticity diagram to the
actually-measured color coordinate meets a contour line of the CIE
1976 chromaticity diagram. It should be noted that a peak
wavelength is different from the dominant wavelength. The peak
wavelength has the highest energy intensity. The peak wavelength is
a wavelength value indicating the highest intensity in the spectrum
graph of the actually-measured output light, regardless of
luminosity.
[0039] Here, the blue LED chip 103 has a dominant wavelength of 443
to 455 nm. The red phosphor 107 has a color coordinate falling
within a quadrilateral space defined by four coordinate points
(0.5448, 0.4544), (0.7079, 0.2920), (0.6427, 0.2905) and (0.4794,
0.4633), based on the CIE 1931 color chromaticity diagram. The
green phosphor 105 has a color coordinate falling within a
quadrilateral space defined by four coordinate points (0.1270,
0.8037), (0.4117, 0.5861), (0.4197, 0.5316) and (0.2555, 0.5030).
Accordingly, a liquid crystal display (LCD) device employing the
white light source module 510 for a backlight unit may exhibit high
color reproducibility across a very large color coordinate space
covering a substantially entire s-RGB space on the CIE 1976
chromaticity diagram (see FIG. 7). This high color reproducibility
is hardly attainable from a conventional combination of a blue LED
chip and red and green phosphors.
[0040] The blue LED chip and red and green phosphors falling
outside the dominant wavelength range and color coordinate space as
described above may degrade color reproducibility or color quality
of the LCD. Conventionally, the blue LED chip used along with the
red and green phosphors to obtain white light has a dominant
wavelength of typically 460 nm or more. However, according to the
present embodiment, the blue light has a shorter dominant
wavelength than the conventional one and the red and green
phosphors have a color coordinate falling within the quadrilateral
space as described above, thereby producing higher color
reproducibility which is hardly achieved by the prior art.
[0041] The blue LED chip 103 may adopt a group-III nitride
semiconductor LED device in general use. Also, the red phosphor 107
may utilize a nitride phosphor such as CaAlSiN.sub.3:Eu. This
nitride red phosphor is less vulnerable to the external environment
such as heat and moisture than a yellow phosphor, and less likely
to be discolored. Notably, the nitride red phosphor exhibits high
excitation efficiency with respect to the blue LED chip having a
dominant wavelength set to a specific range of 443 to 455 nm to
obtain high color reproducibility. Other nitride phosphors such as
Ca.sub.2Si.sub.5N.sub.8:Eu or the yellow phosphor such as
(Ca,Sr)S:Eu may be utilized as the red phosphor 107. The green
phosphor 105 may adopt a silicate phosphor such as
A.sub.2SiO.sub.4:Eu where A is at least one of Ba, Sr and Ca. For
example, the green phosphor 105 may employ
(Ba,Sr).sub.2SiO.sub.4:Eu. The silicate phosphor demonstrates high
excitation efficiency with respect to the blue LED chip having a
dominant wavelength of 443 to 455 nm. Alternatively, one of
SrGa.sub.2S.sub.4:Eu and .beta.-SiAlON (Beta-SiAlON) may be
utilized as the green phosphor 105.
[0042] Particularly, the blue LED chip 103 has a full width at half
maximum (FWHM) of 10 to 30 nm, the green phosphor 105 has a FWHM of
30 to 100 nm, and the red phosphor 107 has a FWHM of 50 to 200 nm.
The light sources 103, 105, and 107 with the FWHM ranging as
described above produces white light of better color uniformity and
higher color quality. Especially, the blue LED chip 103 having a
dominant wavelength of 443 to 455 nm and a FWHM of 10 to 30 nm
significantly enhances excitation efficiency of the
CaAlSiN.sub.3:Eu or (Ca,Sr)S:Eu red phosphor and the
A.sub.2SiO.sub.4:Eu, SrGa.sub.2S.sub.4:Eu, or .beta.-SiAlON green
phosphor. Here, A in A.sub.2SiO.sub.4:Eu is at least one of Ba, Sr,
and Ca.
[0043] According to the present embodiment, the blue LED chip has a
dominant wavelength of a predetermined range and the green and red
phosphors have color coordinates within a predetermined space. This
allows superior color reproducibility than a conventional
combination of the blue LED chip and yellow phosphor, and than a
conventional combination of the blue LED chip and green and red
phosphors, respectively. This also improves excitation efficiency
and overall light efficiency as well.
[0044] Furthermore, according to the present embodiment, unlike the
conventional white light source module using the red, green and
blue LED chips, a fewer number of LED chips are required and only
one type of the LED chip, i.e., blue LED chip is required. This
accordingly reduces manufacturing costs for packages and simplifies
a driving circuit. Notably, an additional circuit may be configured
with relative simplicity to increase contrast or prevent blurring.
Also, only one LED chip 103 and the resin encapsulant encapsulating
the LED chip 103 allow white light of a unit area to be emitted,
thereby ensuring superior color uniformity to a case where the red,
green and blue LED chips are employed.
[0045] FIG. 3 is schematic cross-sectional view illustrating a
white light emitting device 200 and a white light source module 520
using the same. In the embodiment of FIG. 3, a blue LED chip 103 is
directly mounted on a circuit board 101 by a chip-on-board
technique. The blue LED chip 103 constitutes the white light
emitting device 200 of a unit area together with a red phosphor and
a green phosphor excited by the blue LED chip 103. Moreover, to
achieve maximum color reproducibility, the blue LED chip 103 has a
dominant wavelength range, and the red phosphor and green phosphor
have a color coordinate space as described above, respectively.
That is, the blue LED chip 103 has a dominant wavelength of 443 to
455 nm. The red phosphor has a color coordinate falling within a
quadrilateral space defined by four coordinate points (0.5448,
0.4544), (0.7079, 0.2920), (0.6427, 0.2905) and (0.4794, 0.4633) on
the CIE 1931 color chromaticity diagram. The green phosphor has a
color coordinate falling within a quadrilateral space defined by
four coordinate points (0.1270, 0.8037), (0.4117, 0.5861), (0.4197,
0.5316) and (0.2555, 0.5030).
[0046] However, according to the present embodiment, the red and
green phosphors are not dispersed and mixed in a resin encapsulant
but provided as a phosphor film. Specifically, as shown in FIG. 3,
a green phosphor film 205 containing the green phosphor is thinly
applied along a surface of the blue LED chip 103 and a
semi-circular transparent resin encapsulant 230 is formed on the
green phosphor film 205. Also, a red phosphor film 207 containing
the red phosphor is applied on a surface of the transparent resin
encapulant 230. The green phosphor film 205 and the red phosphor
film 207 may be located reversely with each other. That is, the red
phosphor film 207 may be applied on the blue LED chip 103 and the
green phosphor film 205 may be applied on the resin encapsulant
230. The green phosphor film 205 and the red phosphor film 207 may
be formed of a resin containing green phosphor particles and red
phosphor particles, respectively. The phosphors contained in the
phosphor films 207 and 205 may employ one of a nitride, a yellow
phosphor and a silicate phosphor as described above.
[0047] As described above, in the white light emitting device 200,
the green phosphor film 205, the transparent resin encapsulant 230,
and the red phosphor film 207 are formed to further enhance color
uniformity of white light outputted. When the green and red
phosphors (powder mixture) are merely dispersed in the resin
encapsulant, the phosphors are not uniformly distributed due to
difference in weight between the phosphors during resin curing,
thus risking a problem of layering. This may reduce color
uniformity in a single white light emitting device. However, in a
case where the green phosphor film 205 and the red phosphor film
207 separated by the resin encapsulant 230 are adopted, the blue
light emitted at various angles from the blue LED chip 103 are
relatively uniformly absorbed or transmitted through the phosphor
films 205 and 207, thereby producing more uniform white light
overall. That is, color uniformity is additionally enhanced.
[0048] Also, as shown in FIG. 3, the phosphor films 205 and 207
separate from each other by the transparent resin encapsulant 230
may lower phosphor-induced optical loss. In a case where the
phosphor powder mixture is dispersed in the resin encapsulant,
secondary light (green light or red light) wavelength-converted by
the phosphor is scattered by phosphor particles present on an
optical path, thereby causing optical loss. However, in the
embodiment of FIG. 3, the secondary light wavelength-converted by
the thin green or red phosphor film 205 or 207 passes through the
transparent resin encapsulant 230 or is emitted outside the light
emitting device 200, thereby lowering optical loss resulting from
the phosphor particles.
[0049] In the embodiment of FIG. 3, the blue LED chip has a
dominant wavelength range, and the green and red phosphors have
color coordinate space as described above, respectively.
Accordingly, the white light source module 520 for the BLU of the
LCD exhibits high color reproducibility across a very large space
covering a substantially entire S-RGB space. This also reduces the
number of the LED chips, and manufacturing costs for driving
circuits and packages, thereby realizing lower unit costs. Of
course, the blue, green and red light may have a FWAH ranging as
described above.
[0050] In the present embodiments described above, each of LED
chips is directly mounted on the circuit board by a COB technique.
However, the present invention is not limited thereto. For example,
the LED chip may be mounted inside a package body mounted on the
circuit board. FIGS. 4 and 5 illustrate additional package bodies
employed according to an exemplary embodiment of the invention,
respectively.
[0051] FIG. 4 is a cross-sectional view illustrating a white light
emitting device 300 and a white light source module 530 using the
same according to an exemplary embodiment of the invention.
Referring to FIG. 4, a package body 310 defining a reflective cup
is mounted on a circuit board 101. A blue B LED chip 103 is
disposed on a bottom of the reflective cup defined by the package
body 310 and a resin encapsulant 330 having a green R phosphor 105
and a red G phosphor 107 dispersed therein encapsulates the LED
chip 103. To attain a surface or line light source with a desired
area, a plurality of the white light emitting devices 300, i.e., a
plurality of the LED packages may be arranged on the board 101.
[0052] Also in the embodiment of FIG. 4, the blue LED chip has a
dominant wavelength range, and the red and green phosphors have
color coordinate spaces as described above, respectively, thereby
assuring high color reproducibility. Furthermore, the number of the
LED chips, and manufacturing costs for driving circuits and
packages are declined to realize lower unit costs.
[0053] FIG. 5 is a schematic cross-sectional view illustrating a
white light emitting device and a white light source module 540
using the same according to an exemplary embodiment of the
invention. Referring to FIG. 5, as in the embodiment of FIG. 4, the
white light emitting device 400 includes a package body 410
defining a reflective cup and a blue LED chip 103 mounted on the
reflective cup.
[0054] However, according to the present embodiment, the red and
green phosphors are not dispersed and mixed in a resin encapsulant
and provided as a phosphor film. That is, one of a green phosphor
405 and a red phosphor 407 is applied along a surface of the blue
LED chip 103 and a transparent resin encapsulant 430 is formed
thereon. Also, the other one of the green and red phosphors 405 and
407 is applied along a surface of the transparent resin encapsulant
430.
[0055] As in the embodiment of FIG. 3, in the embodiment of FIG. 5,
the green phosphor film 405 and the red phosphor film 407 separated
from each other by the resin encapsulant 430 are employed to ensure
superior color uniformity. Also, in the same manner as the
aforesaid embodiments, the blue LED chip has a dominant wavelength
range and the red and green phosphors have color coordinate spaces
as described above, thereby producing high color reproducibility
across a very large space covering a substantially entire s-RGB
space.
[0056] FIG. 7 illustrates the CIE 1976 chromatic diagram indicating
color coordinate ranges obtained in a case where white light source
modules of Inventive Example and Comparative Example are employed
in BLUs of LCDs, respectively.
[0057] Referring to FIG. 7, the white light source module of
Inventive Example emits white light by a combination of a blue LED
chip, a red phosphor and a green phosphor (see FIG. 4). In the
white light source of Inventive Example, the blue LED chip has a
dominant wavelength of 443 to 455 nm, particularly 451 nm. Also,
the red phosphor emits red light having a color coordinate falling
within a quadrilateral space defined by four coordinate points
(0.5448, 0.4544), (0.7079, 0.2920), (0.6427, 0.2905) and (0.4794,
0.4633) based on the CIE 1931 color chromaticity diagram. The green
phosphor emits green light having a color coordinate falling within
a quadrilateral space defined by (0.1270, 0.8037), (0.4117,
0.5861), (0.4197, 0.5316) and (0.2555, 0.5030) based on the CIE
1931 color chromaticity diagram.
[0058] Meanwhile, the white light source module of Comparative
Example 1 emits white light by a combination of red, green and blue
LED chips. Also, a white light source module of Comparative Example
2 emits white light using a conventional cold cathode fluorescent
lamp.
[0059] The chromaticity diagram of FIG. 7 indicates a color
coordinate space of the LCD employing the light source module of
Inventive Example as the BLU, and a color coordinate space of the
LCDs employing the light sources of Comparative Example land
Comparative Example 2 as the BLUs, respectively. As shown in FIG.
7, the LCD adopting the BLU according to Inventive Example exhibits
a very broad color coordinate space covering a substantially entire
s-RGB space. This high color reproducibility is not attainable by a
conventional combination of a blue LED chip, red and green
phosphors.
[0060] The LCD utilizing the BLU (RGB LED BLUE) according to
Comparative Example 1 employs only the LED chips as red, green and
blue light sources, thus demonstrating a broad color coordinate
space. However, as shown in FIG. 7, the LCD adopting the RGB LED
BLU according to Comparative Example 1 disadvantageously does not
exhibit a blue color in the s-RGB space. Also, only three-color LED
chips employed without phosphors degrade color uniformity, while
increasing the number of the LED chips required and manufacturing
costs. Notably, this entails complicated configuration of an
additional circuit for contrast increase or local dimming, and
drastic increase in costs for the circuit configuration.
[0061] As shown in FIG. 7, the LCD employing the BLU (CCFL BLU) of
Comparative Example 2 exhibits a relatively narrow color coordinate
space, thus lowered in color reproducibility over the BLUs of
Inventive Example and Comparative Example 1, respectively.
Moreover, the CCFL BLU is not environment-friendly and can be
hardly configured in a circuit for improving its performance such
as local dimming and contrast adjustment.
[0062] As set forth above, according to exemplary embodiments of
the invention, a blue LED chip having a dominant wavelength of a
specific range, and red and green phosphors having a color
coordinate of a specific space, respectively, are employed. This
assures high color reproducibility which is hardly realized by a
conventional combination of a blue LED chip, red and green
phosphors. This also results in superior color uniformity and
reduces the number of the LEDs necessary for a light source module
for a BLU, and costs for packages and circuit configuration. In
consequence, this easily produces a higher-quality and lower-cost
white light source module and a backlight unit using the same.
[0063] While the present invention has been shown and described in
connection with the exemplary embodiments, it will be apparent to
those skilled in the art that modifications and variations can be
made without departing from the spirit and scope of the invention
as defined by the appended claims.
* * * * *